1. Field of the Invention
The present invention relates to a hot stamping machine of the type comprising a stamping member, which is intended to press hot stamping foil against the peripheral surface of individual articles in order to stamp the articles.
2. Brief Description of the Related Art
In the field of stamping it is known to produce decorative patterns, for example metallic borders, on a plastic material article by means of a stamping machine, in which a stamping foil is pressed between a heated stamping member, which carries the patterns to be produced on the article, and the peripheral surface of the article. If the patterns to be produced are detailed, the width of the stamping foil used for stamping is selected to be as low as possible, in order to limit the stamping foil area which must be scrapped after each stamping and thus to reduce the costs associated with the stamping. However, the handling of a stamping foil of low width on a stamping machine is delicate.
In the case of stamping with a punch which is able to move in translation relative to the machine frame during stamping, or with a stamping wheel, the stamping member comes to press the stamping foil against the peripheral surface of the article to be stamped, which is driven in rotation. Conventionally the stamping foil is therefore moved opposite the stamping member, via unwinding from an unwinding reel which is fixed relative to the machine frame and rewinding onto a rewinding reel which is likewise fixed relative to the machine frame, an appropriate tension in the stamping foil being obtained between these two reels by means of a constant tension device, such as a spring-loaded beating arm. A suitable tension in the stamping foil is more important for a stamping foil of low width, which is particularly sensitive to vibrations or other disturbances which might alter its position relative to the stamping member. However, a constant tension device such as a beating arm generates, due to its inertia, and when the stamping foil is of a low width and the stamping rate is high, a jumping forwards motion of the stamping foil opposite the stamping element, along with a variation in the tension of the stamping foil. Such a variation in the tension of the stamping foil may lead to the appearance of stamping defects on the articles.
When stamping foil rewinding reel is moved with the punch which is able to move relative to the machine frame during stamping, or when the stamping is carried out with a stamping punch which is fixed relative to the frame during stamping, the stamping foil is conventionally fixed opposite the punch during stamping, the article which is to be marked being moved into contact with the punch in such a way as to squeeze the stamping foil between the punch and the peripheral surface of the article. The stamping foil thus undergoes strain when it is rewound, which may damage the stamping foil in the case of a low stamping foil width and a high stamping rate.
Besides, DE-U-94 20 707 discloses a hot embossing machine comprising an embossing cylinder and an underlying impression cylinder, between which an embossing gap is formed. The embossing cylinder is provided along its circumference with a heatable embossing die, which is intended to press a stamping foil against a material layer. In this machine, the speed of the stamping foil in the embossing gap is controlled by a suction rotative control roller, which is arranged upstream from the embossing gap. More precisely, the stamping foil cooperates without sliding with the upstream rotative control roller, whose rotation is controlled by a driving motor, the stamping foil being drawn at a constant speed by a pull device arranged downstream from the embossing gap. Depending on its rotation speed, the upstream rotative roller is thus able to decrease or increase the speed of the stamping foil in the embossing gap relative to the speed which results from the pulling of the downstream pull device. Such a control of the speed of the stamping foil performed by an upstream rotative control roller driven by a motor is satisfactory when the stamping foil continuously moves in the embossing gap, the speed of the stamping foil being simply decreased or increased. However, when the stamping foil is to be moved only sequentially, as it is the case for the stamping of individual articles, the use of a rotative control roller driven by a motor and arranged upstream from the embossing gap is not adapted. In this case, the stamping foil should be rapidly accelerated from a zero speed. In practice, the driving of the stamping foil, notably for a stamping foil of low width, by a rotative roller driven by a motor and arranged upstream from the embossing gap would lead either to the appearance of stamping defects on the articles, due to a too high stamping foil speed causing the stamping foil to accumulate at the stamping member during the stamping, or to the breaking of the stamping foil, due to a too low stamping foil speed causing stamping foil tension peaks. Indeed, in practice, it would be delicate and even impossible to get a perfect synchronisation of the rotation speed of the control roller relative to the movement of the articles being brought successively opposite the stamping member.